Metals, such as cobalt, nickel, and indium are often added to gold plating compositions to increase the hardness of the electrodeposited metal. Provided that the composition of such a bath and the conditions under which it is operated are adequately controlled, bright deposits are readily obtained over a wide range of current densities. The prior art has long recognized the desirability of incorporating such metals into gold plating formulations, exemplary of which are the following U.S. Pat. Nos.: 2,812,299; 3,149,057; 3,149,058; 3,716,463; 3,787,463; 3,856,638; 3,864,222; 3,902,977; 2,905,601; 4,076,598; 4,186,064; 4,197,172; and 4,253,920 (the latter two patents being in the names of applicants, and of common assignment herewith).
While a variety of compounds may be utilized as the means by which the hardening agents are introduced into the plating bath, it has been recognized that considerable advantage can be realized by the utilization of chelated forms of the metals. Thus, U.S. Pat. No. 3,149,057 discloses the addition of the cobalt chelate of ethylenediamine tetraacetic acid; U.S. Pat. No. 3,149,058 teaches the use of the nickel chelate of an amino polycarboxylic acid; U.S. Pat. No. 3,787,463 discloses the use of polyamine sulfite complexes of the metal ions; U.S. Pat. No. 3,856,638 teaches the utilization of cobalt in the form of a complex with amino guanidine; U.S. Pat. No. 3,864,222 teaches the inclusion of compounds or chelates, such as cobalt or nickel sulfates or chelates of base metals with nitrilotriacetic acid or ethylenediamine tetraacetic acid, and the like; U.S. Pat. No. 4,186,064 employs a preformed, fully neutralized salt of a cobalt or nickel organophosphorus chelate; and U.S. Pat. No. 4,253,920 discloses the inclusion of the chelated forms of nickel or cobalt with 1-hydroxyethylidene-1,1-diphosphonic acid.
Generally, in electroplating baths for gold and other metals there is a tendency for contamination with extraneous metals to occur, which can affect the stability of the bath and cause a rapid decrease in the current efficiency at which it operates. In response, phosphonic acid chelating agents have, for example, been proposed for use in such baths, for the purpose of complexing with contaminants such as copper and lead, to thereby reduce or eliminate their deleterious effects. Exemplary of the baths containing such agents are those that are described in U.S. Pat. Nos. 3,770,596; 3,672,969; 3,706,634; and 3,904,493. The use of various organic compounds as brighteners, levelling agents, buffering agents, and the like has, of course, long been known, and the patent and technical literature proposes many compounds and combinations thereof to achieve various effects and advantages. Despite the foregoing, there remains a demand for an all-purpose bath which is stable and resistent to contamination, and which is capable of operating efficiently at high speeds and over a wide range of current densities, to produce hard bright deposits of substantially pure gold.
Accordingly, it is an object of the present invention to provide a novel gold plating bath containing a cobalt, nickel, and/or indium hardener, which is stable and efficient over wide ranges of current density, pH values and temperatures, and which can be used to excellent advantage for rack, barrel, strip and other high speed applications.
It is also an object of the invention to provide such a bath from which hard gold deposits are produced, which deposits contain a very small amount of the codeposited metal, relative to the high level of hardness achieved.
Another object of the invention is to provide such a bath which can be formulated readily and relatively economically, and which is highly resistant to the effects of metal contamination.
Yet another object of the invention is to provide a novel and highly efficient method for electrodepositing hard, bright gold deposits over wide ranges of current densities, pH values and temperatures, which is well-suited for use in a variety of electroplating techniques and apparatus.